Dual sensor intrusion detection systems are well known in the art. See for example, U.S. Pat. No. 4,401,976 or 4,437,089. A typical dual sensor intrusion detection system comprises a passive infrared radiation (PIR) sensor and a microwave sensor. The sensors are directed to detect an intruder from the same volume of space. To trigger an alarm, however, both of the sensors must simultaneously detect the presence of an intruder. The use of two different types of energy sensing devices directed at the same volume of space to detect the presence of an intruder, renders such a dual sensing intrusion detection system highly intolerant to false alarms.
Increasingly, however, it is necessary to mount or install intrusion detection systems in locations where it is difficult or expensive to supply wires for electrical power or alarm conditions. Thus, the intrusion detection system must be self-contained. This requires the use of batteries.
However, it should be appreciated that with batteries, the dual sensor intrusion detection system of the prior art is constantly on. This renders the battery powered dual sensor intrusion detection system useless, because as a practical matter, batteries must be changed so frequently.
U.S. Pat. No. 4,437,089 discloses two detectors with the sensitivity of one detector increased when the other detector detects an intruder. However, that reference does not disclose or teach activating a second detector only when there is a detection by the first detector to reduce power consumption.